1. Field of the Invention
The present invention relates to a gas generator composition used in a gas generating apparatus for inflating an air bag.
2. Description of the Related Art
Air bags are often used as a device in automobiles to protect the automobile's occupants in case of a collision. When used for this purpose, the air bag is often attached to the steering wheel in the automobile passenger compartment and operates by generating gas to inflate a bag between the steering wheel and the driver. Conventional gas generators primarily contain sodium azide and various types of oxidizing agents as primary chemical agents. When burned, these agents generate nitrogen gas that inflates the air bag. The particular apparatus used to inflate the air bag is known as a gas generator container.
Because sodium azide when burned generates clean nitrogen gas, it has become a popular choice as the primary chemical agent for gas generators. Unfortunately, sodium azide is highly toxic and easily forms unstable volatile substances, when exposed to acids or heavy metal. Consequently, special care must be taken in the handling of sodium azide both during its production and after it is spent generating gas. Moreover, gas generators with sodium azide as a primary chemical agent, produce large amounts of corrosive residues such as sodium and sodium compounds. These substances should ideally be neutralized before being discarded.
In order to avoid these problems, efforts have been made to produce gas generators that contain no sodium azide. For example, Japanese Patent Publication No. 20919/1983 discloses a gas generator comprising the following three components: (1) 78 to 92% by weight of a chlorate or perchlorate of an alkali metal or of an alkaline earth metal as an oxidizing agent; (2) 7.9 to 17.2% by weight of cellulose acetate and (3) 0.1 to 0.8% by weight of acetylene black or graphite as a carbon-containing combustion controller. This type of gas generator generates about 0.36 lit/g of gas, that under typical conditions contains includes water, carbon dioxide, oxygen and virtually no carbon monoxide.
Unfortunately, the gas generator composition described in the 20919/1983 publication has a very high combustion temperature. When the composition as described in this publication burns in a gas generator container, the gasses produced must be thoroughly cooled to prevent the air bag from burning. Consequently, a large amount of cooling agent must be provider in the gas generator container. This requirement inhibits efforts to make smaller sized gas generators.
Alternatively, Japanese Patent Publication No. 57150/1982 discloses a gas generator similar to the 20919/1983 publication, but contains azodicarbonamide (hereinafter referred to as ADCA) and an oxohalogeno acid salt.
The composition of this gas generator produces a large volume of gas, but is unstable at low temperatures.
Generally, the amount of the gas generator required per gas generator container can be reduced by increasing the amount of gas generated per unit weight of the gas generator. This presents a straight forward technique to reduce the size and weight of gas generator containers. Present efforts to achieve size and weight reduction of gas generators, however, have yet to take full advantage of this technique.